The present invention is directed to internally mounted bicycle transmissions and, more particularly, to an internally mounted bicycle transmission which employs roller clutches in the transmission path
Internally mounted bicycle transmissions are installed inside the hub shell of the rear wheel of the bicycle and have the following main parts: (a) a fixed shaft which is fastened to the frame of the bicycle, (b) a planetary gear mechanism, (c) one-way clutches, and (d) an operating part. The planetary gear mechanism used in an internally mounted bicycle transmission with a conventional four-speed gear is constructed from (a) three sun gears which are installed around the outer circumference of the fixed shaft, (b) planetary gears which engage with the respective sun gears, and (c) a ring gear which engages with the planetary gears. The respective sun gears can be selectively coupled with the fixed shaft by means of the operating part. The planetary gears are supported by a gear frame which is installed on the outer circumference of the fixed shaft. In addition, respective one-way clutches are installed between the ring gear and the hub shell, and between the gear frame and the hub shell. The transmission ratio is altered by using the operating part to select that sun gear that is coupled to the fixed shaft. When no sun gear is coupled to the fixed shaft, the gear frame and the hub shell are coupled directly to each other.
Conventional one-way clutches used in internally mounted bicycle transmissions have a multiple number of ratchet pawl members which are installed (e.g.) between the ring gear and the hub shell. These ratchet pawl members are ordinarily long, slender members which pivot about one end. By pivoting and engaging with ratchet teeth on the hub shell, these ratchet pawl members transmit the motive force in one direction only.
In the case of idle rotation in the opposite direction from the direction of engagement, the ratchet pawl members pivot and strike the hub shell so that an impact sound is generated. This creates a significant amount of noise. Thereafter, when the system shifts from an idle state to an engaged state, it takes time for the ratchet pawl members to engage with the ratchet teeth, since the amount of play is relatively large. Moreover, since the ratchet pawl members and ratchet teeth engage abruptly, there is a considerable shock instead of a smooth transition. The same is true in the case of changing speeds. Thus, the switching of the one-way clutch cannot be performed in a smooth manner. This is especially true in the case of speed reduction where the pedals must be turned faster after the speed change than before the speed change. The amount of play seems to the cyclist to be amplified by the difference in the transmission ratio, thus aggravating the feeling of a lack of smoothness during the speed change.